Drive device

ABSTRACT

A drive device, especially for a pair of welding tongs comprising a pair of limbs, essentially arranged between the adjusting ends of the limbs, which are located opposite to the welding ends embodied with welding electrodes, for adjusting at least one limb between a welding position and a standby position. In order to improve said type of drive device in such a way that the construction length thereof is small, the drive device can be continuously controlled and monitored for the actuation of the welding tongs, the structure thereof is simple, economical and easy to maintain, and the noise of said drive device is significantly reduced, the inventive drive device is provided with an electric motor-driven screw-thread drive with a rotating nut and a rotating spindle which is axially displaceable between an extended and a return position, said spindle being movingly connected with the free extending end thereof to an adjusting end of the limb. Said drive device can be used as a main drive for a pair of welding tongs for the positioning of the limbs thereof, or can be used as a secondary drive, i.e., as a stopping device for the setting of at least one stopping position of the limb of a pair of welding tongs.

The present invention refers to a drive device for welding tongsparticularly comprising a pair of limbs formed for instance asdouble-armed levers, said drive device being arranged substantiallybetween two adjusting ends of the limbs or levers which are locatedopposite to the welding ends provided with welding electrodes forpivoting at least one limb or lever between the welding position and thestandby position.

Normally, welding tongs with a pneumatic drive device for generating arespective electrode power are used nowadays in industry, for instancein the automobile production. The pneumatic drive devices causes,particularly if the welding tongs are formed with a pair of limbs ordouble-armed levers, these limbs or levers to be moved from theirstandby position into their welding position, in which they oppositelypress onto sheets to be welded together. Upon reaching an adequateelectrode power, a welding current is supplied to the welding tongs andthe welding of the sheets takes place. Subsequently, the limbs of thewelding tongs, hereinafter referred to as levers, are moved back intotheir standby position and the welding tongs are moved for instance bymeans of a robot to the next welding position.

When using welding tongs with a pneumatic drive device it turned outthat the drive is relatively uncomplicated and easy to maintain and canbe controlled and monitored in a simple way. However, the electrodepower in a pneumatic drive device can hardly be controlled during thewelding process. When adjusting the levers to the standby position, thewelding electrodes impinge onto the workpiece. Neither during adjustmentof the levers from the standby position to the welding position nor viceversa during the welding process is a position monitoring of the levelsby means of the drive device possible. The pneumatic operation of thedrive device also leads to a high noise level and great effort for theinstallation of the respective pneumatic supply system. Moreover, airpermanently escapes, which leads to a further noise pollution.

Moreover, it must be noted that the pneumatic drive device'sconstruction length between the adjustment lever ends is relativelylarge. The construction length is, however, important in connection withthe maximum possible opening angle of the levers. That means that if theconstruction length of the drive device and the lever length ispredefined, the maximum opening angle of the level in the standbyposition results, which is variable only by changing the constructionlength or the lever length. The size of the maximum opening angle isimportant to be able to move the welding tongs from one welding positionto the other without colliding with the workpiece.

In view of the above-mentioned prior art, the subject matter of theapplication is based on the object to improve the drive device forwelding tongs in that these tongs have a small construction length, thedrive device can substantially be controlled and monitored in acontinuous manner and has a simple structure, which is cost-effectiveand easy to maintain, wherein the noise pollution by the drive device issignificantly reduced.

This object is solved in connection with the features of the preamble ofclaim 1 in that the drive device comprises an electric motor-drivenscrew thread drive with a rotating nut and a spindle axially adjustablebetween the extended position and the return position, the free extendedend of the spindle being movingly connected to an adjustment end of alimb or lever arm.

The electric motor-driven drive enables the supply of the drive devicein a simple manner via electrical lines. A complex pneumatic supplysystem is not required. Furthermore, the electric motor-driven driveenables that in a simple manner a control of the monitoring of theposition of the welding electrodes or levers of the welding tongs ispossible. This may for instance be implemented by a respectivemonitoring of the relative arrangements of rotating nut and spindle.Moreover, the electrode power can easily be monitored or adjustedbefore, during and after termination of the welding process. Accordingto the invention it is also possible to adjust any intermediate positionbetween the welding position and the standby position so that the levers(limbs) of the welding tongs when moving towards a further welding pointmust not necessarily be pivoted back into the standby position. In thisconnection is may be sufficient if the levers and thus the weldingelectrodes are spaced apart to such an extent that a movement of thewelding tongs to the next welding point is possible.

The electric motor-driven drive with a screw thread drive according tothe invention is extremely quiet, simple and has a cost effectivedesign. Moreover, a small construction length between the adjustmentlever ends results, since the spindle in its return position onlyslightly projects over the rotating nut.

In order to refrain from using expensive bearing means for the rotatingnut, this nut can be formed with an integrated radial and axial bearingmeans.

In order to obtain a favourable mechanic efficiency as a result of lowrolling friction, substantially no stick-slip effect and a low wear thusleading to a long life, the screw thread drive is formed as a ballscrew. Such a ball screw further comprises a high positioning andrepetition accuracy as well as a high path feed rate. Of course, it isalso possible that different screw thread drives are used, such as atrapezoidal thread, planetary gear train or the like or also a piniondrive or the like.

In order to protect the screw thread drive to the greatest possibleextent from being soiled, the drive device may have a sleeve-shapeddrive housing with a holding shoulder at least partially revolvingtherein, wherein the rotating nut is held rotatable at the holdingshoulder but is supported in an axially unmovable manner. It must benoted that accordingly the spindle is substantially arranged in thedrive housing at least in its return position. The holding shoulderrevolving in the inside of the drive housing may also be formed as afully revolving substantially radially inwardly projecting holdingshoulder.

The invention can be used in C-shaped welding tongs, X-shaped weldingtongs or also other welding tongs.

In order to be able to simply attach the rotating nut within the drivehousing, a bearing ring may be fixed for co-rotation with the holdingshoulder or it may be connected to the shoulder in a detachable manner,wherein the rotating nut is rotary relative to the bearing ring. Thebearing ring may in this connection be set onto the outside of therotating nut and it may be supported in a rotary manner relative to samee.g. by means of adequate ball bearings, or it may be supported in anaxially immovable manner. In this connection, the bearing ring formspart of the radial and axial bearing means for the rotating nut, whereinthe support can be implemented by axial bearings, angular ball bearings,rolling bearings, needle bearings or the like, wherein these bearingsmay also be arranged in pairs.

In order to further improve the position accuracy and reproducibility ofadjustment of the screw thread drive, the rotating nut may be preloadedfor a support free from backlash.

In order to obtain an electric motor-driven drive that can well becontrolled and supplied, this drive may be an especially brushless servomotor. However, other DC motors or the like may also be used instead ofa servo motor.

In order to obtain a favourable accessibility of the drive device e.g.for maintenance purposes, the drive housing may be closed by a coverparticularly in a detachable manner on the housing end opposing the freeextended end of the spindle.

In order to be able to design the electric motor-driven drive in acompact manner in order to reduce the construction length, the servomotor may comprise a stator arranged within the drive housing in amanner particularly fixed for co-rotation, and a rotor rotatablyarranged therein, which is movingly connected to the rotating nutparticularly in a non-positive way.

The construction length can further be reduced in that the rotor isformed as a rotor sleeve into which the spindle is at least partiallyretracted in its return position. That means that in the return positionof the spindle, the rotor sleeve surrounds the spindle in a manner thatthe servo motor forms part of the return space of the spindle.

A simple movement connection between rotating nut and rotor sleeve canbe seen in that the rotor sleeve is fixed for co-rotation with therotating nut particularly at its front side at the first end of therotor sleeve pointing away from the cover.

In order to be able to determine in a simple and compact manner theposition of the rotor sleeve and the rotating nut connected therewithand thus also the spindle, a position transmitter may be associated tothe rotating nut and/or the rotation sleeve. By this positiontransmitter the respective rotary position of the rotary sleeve andaccordingly the rotary position of the rotating nut can be determined.If the rotary position of the rotating nut is known, the adjustment ofthe spindle can also be determined.

In order to be able to directly correlate the measured value with arespective rotary position of the rotor sleeve or rotating nut, theposition transmitter may be an absolute value transmitter. Such anabsolute value transmitter may e.g. digitally-absolutely measure theposition. Other position transmitters are also possible, which carry outan analogue measuring, such as a resolver or the like.

In order to be able to connect the spindle and the adjusting lever endof the respective lever with one another in a simple way, a bearingblock may be arranged as a bearing means for the adjusting lever end atthe extended end of the spindle particularly in a detachable manner.

In order to de-couple the rotary movement of the spindle upon itsadjustment by the rotating nut from the pivoting of the lever, theextended end of the spindle must be fixed for co-rotation in the bearingblock.

In order to protect the screw thread drive particularly during extensionof the spindle from being soiled and in order to protect a worker from apossible injury caused by the screw thread drive, a protective meansvariable in length surrounding the spindle may be arranged between thebearing block and the holding shoulder. This protective means fullysurrounds the spindle and extends up to the drive housing.

A simple example for such a protective means is if the protective meansis formed as a bellows.

A further possibility for a protective means is a helical spring cover.This cover is formed by a thin, wound-up sheet or the like which can behelically extended, wherein one end is attached directly or indirectlyat the bearing block and the other end is substantially attacheddirectly or indirectly on the holding shoulder. Such a helical springcover for instance has the advantage that it is insensitive to sweatdroplets.

In order to keep the bellows at a distance to the rotating nut, this nutcan be surrounded by a substantially hat-like cover on its end pointingtowards the extended end of the spindle, said cover sealingly contactingthe outer periphery of the spindle. In this connection it must be notedthat the hat-shaped cover does not have to extend fully in thecircumferential direction around the rotating nut but can also be formedfor instance essentially bracket-shaped.

The cover may particularly detachably be attached on a side of theholding shoulder pointing away from the bearing ring. Moreover, the partof the cover that contacts the outer periphery of the spindle may at thesame time be used as a lubricant supply means.

In order to be able to support the adjusting lever end of the otherlever in a simple manner at the drive device, the cover may comprise asecond bearing block as a bearing means for supporting the adjustinglever end of the further lever.

In order to simply enable an appropriate pivoting of the levers whenadjusting the spindle, each bearing block may have a transverse boreextending substantially perpendicular to the longitudinal axis of thespindle, in which said transverse bore a shaft particularly detachablyconnected to the respective adjusting lever end is rotatably supported.An rotatable support may in this connection be implemented by a numberof bearings such as separable bearings, cross roller bearings, radialball bearings and the like. It is also possible that a plurality ofthese bearings are provided.

In order to support the shaft with a high bearing capacity and to alsoreceive axial forces, at least two taper roller bearings or separablebearings may be set onto the shaft in a laterally reversed manner.

To enable in this connection a bearing of the adjusting lever endsubstantially free from backlash, each taper roller bearing mayparticularly be pre-loaded by means of a thread ring.

A simple possibility of such a clamping can be realized in that opposingabutment sections for the taper roller bearings are arranged within thetransverse bore and/or on the shaft.

In order to be able to attach the adjusting lever ends in a simplemanner to the respective bearings or bearing blocks, particularlydetachably fixed insertion caps may be arranged on both sides of thetransverse bore at the shaft. These caps may particularly compriseconical attachment bores. These insertion caps serve for attaching theadjusting lever ends at the bearing block. The adjusting lever ends mayparticularly be shaped in a forklike manner so that an attachment of thefork ends on both sides of the transverse bore can be implementedthrough the insertion caps.

The conical attachment bores particularly serve for the fact thatrespective shaft ends of the shaft arranged in the transverse bore arereceived by them, wherein the conical design of the attachment boreensures a fixed seat of the shaft, but at the same time also enables asimple release of the insertion caps.

In order to clamp the taper roller bearings when attaching the insertioncaps, an intermediate ring that can be screwed onto the shaft may existas a lateral, adjustable abutment surface for a taper roller bearing.That means that for instance a taper roller bearing is clamped by therespective, above-mentioned abutment shoulders, whereas the second taperroller bearing laterally reversed thereto is clamped only by attachmentof the respective insertion cap and particularly by the lateral abutmentsurface of the intermediate ring screwed-on.

In order to secure the intermediate ring in its screwed-on position, asafety sheet can be arranged between the insertion cap and theintermediate ring.

The possibility exists that the insertion cap has a cross section in itsaxial direction at least at one portion onto which a respectiveadjusting lever end can be plugged on in a positive-fit manner. Anexample for such a cross section is an angular cross section, such asquadrangular, pentagonal or hexagonal. In order to improve theconnection between the insertion cap and the shaft, the insertion capmay have at least one screw bore for attachment on the shaft.

In order to additionally prevent the adjusting lever end from slidingdown, the insertion cap may have a substantially radially outwardlyprojecting abutment flange on its end pointing away from the shaft. Thatmeans that the adjusting lever end or its fork end is arranged betweenthe abutment flange and the lateral openings of the transverse bore.

In order to enable a higher power load of the drive device, cooling ribsmay be arranged on the outside of the drive housing.

When retracting and extending the spindle and when correspondinglyoperating the welding tongs, tilt momentums in the area of the drivemeans may occur. In order not to transfer them onto the screw threaddrive, at least two guide rods may be arranged substantially in parallelto the longitudinal axis of the spindle, said guide rods being attachedat least at their ends with the drive housing and/or the bearing means.

In order to form the drive device according to the invention morecompact and in order to be capable of well receiving the tilt momentums,each guide rod may be guided in a longitudinal bore within the drivehousing. At its ends the guide rod in the longitudinal bore is e.g.clamped by screws or the like screwed on.

In order to well receive the tilt momentums, the longitudinal bores maysubstantially be arranged in extension of the adjusting lever ends. Ifthe adjusting lever ends are formed in a fork-like manner, a respectivelongitudinal bore with a guide rod may be arranged in extension of eachfork.

According to the invention it results from the previous features thatthe drive device is formed in an extremely compact manner and as asubstantially integrated unit with a screw thread drive, an electricmotor-driven drive and a bearing means for the adjusting lever ends.

In order to be able to supply in such a compact unit sufficientlubricant to all moving parts, a respective lubricant supply system withat least one lubricant supply channel may advantageously be integratedwithin the drive housing and/or the bearing means. In this connection,the possibility also exists that a lubricant distribution system for allmovable parts within the drive housing and within the bearing housing isprovided, see the description of the bearing blocks with the transversebore, shaft and taper roller bearing.

In another embodiment of the invention, the spindle may be arranged in aspindle sleeve, which is rotatably connected to the rotating nut. Thespindle sleeve protects the spindle and it is longitudinally adjustablein this sleeve between its extended and its return position.

In order to be able to support the rotor in a simple manner in theprevious embodiments, the rotor may be arranged on the outside of thespindle sleeve. The stator is arranged in accordance with the drivehousing so that the rotor is rotary together with the spindle sleeve andthe rotating nut.

In order to lock the spindle sleeve on its end opposing the rotatingnut, the rotary cap may be attached at this end of the spindle sleeve ina particularly releasable manner. The releasable attachment leads to afacilitated accessibility to the interior of the rotary sleeve and thusfor instance to the spindle.

In order to be able to rotatably support the spindle and thus therotating nut with respect to the drive housing in a simple manner, atleast one bearing means may be arranged between the spindle sleeve andthe drive housing. An example for such a bearing means are ball bearingsor roller bearings, wherein double-row bearings, such as double-rowseparable bearings or the like have further advantages.

In order to fix the spindle sleeve in the longitudinal direction withrespect to the bearing means, the bearing means may be arranged betweena radially outwardly projecting step section of the spindle sleeve andan intermediate ring. The intermediate ring may be screwed onto theouter side of the spindle sleeve or it may be attached releasable in adifferent manner.

In order to support the spindle sleeve also in the area of its stepsection adjacent to the rotating nut, an attachment ring that mayparticularly be screwed on can be associated to the step section of thespindle sleeve. This attachment ring is e.g. attached in the interior ofthe drive housing, particularly on a holding shoulder projectingradially towards the inside. The attachment may be implemented viascrews or other means.

In order to ventilate the protective means when retracting and extendingthe spindle, a ventilation means may be associated to the protectivespindle. This means comprises for instance air-pervious, porous membersmade of plastics or metal, arranged in the cover, said memberscommunicating through respective lines with the interior of theprotective means. An air exchange takes place through these lines andthe porous members substantially acting as air exchange attenuators, sothat during each extension of the protective means fresh air (cool) maybe sucked into the drive device or actuator device for cooling and isdischarged as heated exhaust air during each retraction.

The invention further refers to welding tongs having at least two limbsmovable relative with respect to each other and provided on the weldingends with an electrode or counter electrode, said limbs may be formed asdouble-armed levers, and a fixing means associated to the operating endsof the limbs opposing the welding ends, wherein a releasable fixingmeans for defining at least one fixing position of this limb is arrangedbetween at least one limb or lever and a fixed point.

Welding tongs of this type are known from DE 195 34 845 C1. The knownwelding tongs are formed as so-called scissors welding tongs with twolimbs. The limbs can be pivoted by means of a joint relative to oneanother. The joint and thus the welding tongs can be pivoted through apivot bolt.

On their welding ends the respective limbs are provided with anelectrode or a counter electrode. The respective sheet members ofparticularly spatially designed bodies are welded by means of theseelectrodes, wherein the welding tongs are usually attached at aprogram-controlled robot or the like. For the relative movement of thelimbs a drive means is associated to the operating ends of the limbsopposing the welding ends. This device is pneumatically or hydraulicallyoperable regarding the welding tongs known from DE 195 34 845 C1.

Furthermore, a releasable locking means is arranged between a fixedpoint provided on a base plate of the welding tongs and at least onelimb. Through this locking means at least one locking position of therespective limb can be defined. The locking means is formed as adouble-acting actuator cylinder with a piston and it may be operatedpneumatically or hydraulically.

The disadvantage in these known welding tongs is that the locking meansthrough the hydraulic or pneumatic operation can basically define a limbin one certain fixing position only. That means that the respective limbis either fixed or it is pivotal. A variation of the locking position orselectable locking positions are not possible. Furthermore, thepossibility does not exist to slightly vary the locking position oncechosen if this becomes necessary before, during or after the weldingoperation of the welding tongs.

To also reproducibly enable in a simple manner a precise and variableadjustment of different locking positions, the locking means may be anelectrically operated actuator means with a variable adjustment of thelocking position. By the selection of the actuator means, differentlocking positions by respective electric operations of the actuatormeans can simply be realized. Moreover, locking positions once taken canalso me minimally varied in a simple manner in case this becomesnecessary. Due to the electric drive of the actuator means this iseasily reproducible and it can be controlled precisely for adjusting arespective locking position.

Moreover, an expensive pneumatic or hydraulic supply system is no longerrequired when using the electric operation of the actuator means.

A simple embodiment of such an electrically operated actuator means canbe seen in that it is formed as a drive device, as described above.

According to the invention, a tongs compensation can be carried out bythe actuator means particularly before and/or after a welding process.That means that before or after the welding process a respective fixedlimb is pivoted about the measure of a tongs compensation.

It would be possible that the drive device is operated pneumatically orhydraulically. However, the entire structure of the drive device canfurther be simplified if it comprises in the same manner an electricallydriven screw thread drive with a rotating nut and an axially adjustablespindle between the extended and the return position, said spindle beingmovingly connected with its free extended end with an adjusting end of alimb. This leads to a small construction length of the welding tongs.The drive device can be controlled and monitored substantiallycontinuously for operating and/or locking the welding tongs, i.e. forpivoting the limbs, and the entire structure is simplified so that thewelding tongs are relatively cost effective and easy to maintain.Moreover, it is noticeable with respect to pneumatically orhydraulically operated drive devices that at the same time the noisepollution is significantly reduced in electrically operated drivedevices.

There is a possibility that the drive device and the actuator means areseparate means arranged at different locations of the welding tongs. Thedrive device may for instance extend as a first drive between theactuator ends of the limbs while the actuator means as a second drive ismovingly connected with one limb at a spacing to its adjusting ends. Inthis manner are the drive device and the actuator means separate and canbe operated and controlled independent of each other.

To further facilitate the structure of the welding tongs, the drivedevice and the actuator means may be integrated in an electricallyoperable adjusting means, which comprises particularly two adjustingelements movable independent of one another, one of which being movinglyconnected to the adjusting end of a limb. By the fact that the adjustingends are movable independently, an adjusting or pivoting of the limbs ispossible and on the other hand a limb can also be arranged in aselectable locking position.

A preferred embodiment of such an adjusting means can be seen in thefact that the adjusting means comprises two screw thread drives, whereina respective adjusting element is movable in the axial direction of aspindle of the respective screw thread drive by each of the screw threaddrives. The screw thread drives can be controlled differentlyelectrically so that the limbs are adjustable independent of each otherand for instance one limb can be fixed in a certain locking positionwhereas the other limb is movable even farther.

If the limbs are movable in the above described manner independent ofeach other, it can further be regarded as being favourable if each ofthe limbs is movable without a flexible connection of the limbs to oneanother by one adjusting element and can possibly be fixed in a selectedlocking position. That means that each limb is adjustable in the axialdirection of the associated revolving spindle or rotary spindle and eachlimb is adjustable when moving towards a welding position for passing-byobstacles. Thus, it is for instance possible to be able to move quickerbetween different welding positions by means of a program-controlledrobot. Moreover, it is easily possible to monitor the contact pressurefor welding, the pressure during welding or the like to be able to carryout in a simple manner a possibly required readjustment of therespective limbs particularly during the welding process.

The possibility exists that the screw thread drives provided for eachlimb have a different design, which could for instance result from thedifferent thread pitches of the spindles. Due to such differentlystructured screw thread drives, the limbs are movable for instancedifferently fast at an identical number of revolutions of the spindles.To simplify the welding tongs with respect to structure, spare partstock etc. the screw thread drives may have a similar design. Anidentical spindle, an identical rotating nut or the like can forinstance be used for both screw thread drives.

According to the invention the possibility exists that the adjustingelements of the adjusting means are not movable fully independently fromone another but can move for instance only at different speeds. This canbe achieved in that the adjusting means has a spindle with at least twodifferent spindle sections, wherein an adjusting element is associatedto each spindle section. These different spindle sections may forinstance be characterized by different thread pitches, wherein thethreads have different rotational directions in the respective spindlesection. The possibility also exists that the thread pitch in thespindle sections is identical and only the rotational direction of thethread is opposed.

In order to be able to precisely determine with the adjusting means inwhich position the respective limb is arranged, a position sensor may beassociated to each adjusting means.

The possibility also exists that the electrically operated actuatormeans is an electric linear drive with e.g. a reaction rail and aprimary portion.

At this point it must additionally be noted that particularly in theautomobile industry, quality measurements are carried out and recordedfor a longer period of time for each screw or welding point inconnection with fastening by means of screws, welding or the like. It ispossible according to the invention to make measuring statements aboutthe different welding points, since it is for instance possible tomeasure and record the electrode power, changes of the electrode powerduring the welding process etc. for each welding point. The electrodepower is measurable directly by the motor current of the servo motor oralso by further power measuring means such as strain gages, load cellsor the like in the area of the drive device. In the same manner can achange of the electrode power during the welding process be measured andmonitored. Moreover, it is easily possible according to the invention toposition the welding electrodes extremely precisely and to track theme.g. for maintaining a certain electrode power.

For such quality statements about the different welding points it is,however, also required that the bearing means between the adjustinglever ends and the drive means are free from backlash. This is enabledby the above-mentioned bearing means with bearing blocks, transversebores, shafts bevel roller bearings, rest shoulders, insertion caps,intermediate ring and safety sheet.

Such a bearing means free from backlash between the adjusting lever endsand the drive means can of course also be used in drive means other thanthe one previously described. The respective bearing means should bearranged at least between an end of the drive device for welding tongsand an adjusting lever end of at least one lever of the welding tongs.

An advantageous embodiment of the invention will now be explained withreference to the Figures of the drawings.

FIG. 1 shows a schematic diagram of a drive device according to theinvention for welding tongs with a control;

FIG. 2 shows a longitudinal cut through the drive device according tothe invention according to FIG. 1;

FIG. 3 shows a longitudinal cut through the drive device according tothe invention rotated 900 with respect to the longitudinal sectionaccording to FIG. 2;

FIG. 4 shows a top plan view onto the drive device according to FIG. 1;

FIG. 5 shows a sub-view of the drive device according to FIG. 1;

FIG. 6 shows a longitudinal section through a further embodiment of thedrive device according to FIG. 1 according to the invention, and

FIG. 7 shows a side view of a drive device and actuator deviceintegrated into an adjusting means.

FIG. 1 shows a schematic diagram of the drive device 1 for welding tongs4 according to the invention with a respective control. The weldingtongs 4 comprise two double-armed levers 2, 3. Respective weldingelectrodes 5 are arranged on an end of each lever designated as weldinglever end 6, 7. The drive device 1 according to the invention isarranged between the adjusting lever ends 8, 9 opposing the weldinglever ends 6, 7. In FIG. 1 in the view with the drawn-through lines, thelevers 2, 3 are in their standby position and in the dotted view thelevers are in their welding position. In the welding position 10 anelectrode power is exerted via the welding electrodes 5 onto a workpiece22 for instance to press two sheets against each other forming theworkpiece for subsequently being welded.

The two levers 2, 3 of the welding tongs 4 are connected to a weldingcontrol. This welding control supplies power to the levers and thus tothe welding electrodes 5 during the welding process. The drive device 1is connected with a motor control 61. By this motor control the drivedevice 1 is controlled for pivoting the levers 2, 3 between the weldingposition 10 and the standby position 11.

At this point it must be noted that any intermediate position betweenwelding and standby position can precisely be adjusted by means of thedrive device according to the invention.

In order to control the welding tongs altogether, the motor control 61and the welding control 63 are connected to a welding tongs control 62.

In order to make a quality statement with respect to each welding point,a quality monitoring means 64 is provided, which is connected to thewelding tongs control 62 and to the motor control 61 for data exchange.By means of the quality monitoring means 64 it is possible to monitorand record for each welding point the electrode power, the position ofthe welding electrodes and the drive device as well as the weldingcurrent and possible changes of these parameters before, during andafter the welding process. The possibility also exists to operate themotor control 61 via the welding tongs control 62 for instance tocontrol the levers of the welding tongs 4 in a desired manner or todetect a welding with a desired quality.

FIG. 2 shows a longitudinal section through the drive device 1 accordingto FIG. 1. For reasons of simplification, the respective adjusting leverends 8, 9 of the levers 2, 3 are not shown or only shown in a schematicdiagram.

The drive device 1 has a sleeve-shaped drive housing 18. This housingcan be closed at one housing end 23 by a cover 24. An absolute valuetransmitter 31 is arranged within the drive housing 18, partially alsowithin the cover 24. For reasons of clarity, the respective supply linesof the absolute value transmitter as well as their further transmissionoutside the drive housing 18 are shown partially only. The absolutevalue transmitter 31 serves for measuring the position of a rotating nut13, which is part of a ball thread drive 12. The rotating nut 13 isrotatably supported at a holding shoulder radially projecting towardsthe inside within the drive housing 18. The rotary support is carriedout via a bearing ring 20 as a radial and axial bearing means, which isdetachably attached on a side of the holding shoulder 19 facing thecover for instance by means of screws. The rotation ring 13 is rotatablebut axially non-displaceably supported in the bearing ring 20.

On the front side 29 facing the cover 24 the rotating nut 13 isdetachably connected to a first end 28 of a rotor sleeve 27 of the servomotor 21 formed as a rotor 26. The connection is implemented via anumber of screws 67, at least one of which being shown in FIG. 2.

On the second end 30 opposing the first end 28 the rotor sleeve 27 ismovingly connected to the absolute value transmitter 31.

A cover 67 is arranged within the rotor sleeve 27 directly adjacent tothe absolute value transmitter 31. The rotor sleeve 27 is partially andparticularly with its second end 30 guided through this cover.

The stator 25 of the servo motor 21 is arranged around the rotor sleeve27 within the drive housing 28. The servo motor is particularly formedas a brush-less motor.

As a further part of the ball screw 12, a spindle 16 is displaceablysupported in the rotating nut 13 between the return position 15, seeFIG. 2, and the extended position 14, see FIG. 3. In its return position15 the spindle 16 is substantially completely arranged within the drivehousing 18. Its extended end 17 still projects from the rotating nut 13,whereas the remaining part of the spindle 16 is located in the rotatingnut 13 or within the rotor sleeve 27. The end opposing the extended end17 of the spindle is arranged in its return position 15 in the area ofthe cover 67.

The extended end 17 of the spindle 16 is connected to a first bearingblock 32 of a bearing means 33, see also FIG. 3. The extended end 17 isfixed for co-rotation within the first bearing block 32.

The spindle 16 is surrounded by a protective means 34 variable in lengthbetween the first bearing block 32 and the holding shoulder 19. Thisprotective means is formed as a bellows 35 connected at its ends withthe bearing block 32 or a cover 37, or it is formed as a helical springcover. The cover 37 covers the rotating nut 13 in a hat-like manner onits end 36 pointing away from the holding shoulder 19. The cover restson the outer periphery 38 of the spindle 16 adjacent to the end 36 ofthe rotating nut. The cover 37 is attached for instance by means ofscrews in the area of the holding shoulder 19 in its side opposing thebearing ring.

A second bearing block 39 is contained in the cover 24 opposite to thefirst bearing block 32. The two bearing blocks are structured as part ofthe bearing means 33 substantially similar to the rotatable bearing ofthe adjusting lever ends 8, 9, see in the respect particularly FIG. 3.

A transverse bore is arranged in each bearing block 32, 39. This boreextends perpendicular to the longitudinal axis 40 of the spindle 16.Within the transverse bore 41 a shaft 42 is rotatably arranged. Therotatable bearing is implemented through a laterally reversedarrangement of two bevel roller bearings 43, 44. In order to fix thebevel roller bearings 43, 44 within the transverse bore 41 and topossibly brace it, appropriate rest shoulders 45, 46 and 47 are providedon the inner periphery of the transverse bore 41 or on the outerperiphery of the shaft 42.

It must be noted that the arrangement of the respective rest shouldersin the first and second bearing block 32, 39 can be made in the reversedmanner so that in the first bearing block 32 the bracing or pretensionof the two bevel roller bearings 43, 44 can be made in FIG. 3 from theright and in the second bearing block 39 in FIG. 3 from the left.

In the first bearing block 32 the bevel roller bearing 43 is fixedbetween the rest shoulders 45 and 46 on the shaft 42 and on thetransverse bore 41. The other bevel roller bearing 44 is held between afurther rest shoulder 47 on the transverse bore 41 and a rest surface 50of an intermediate ring or thread ring 49 fastened on the shaft by meansof screws, particularly for the purpose of pretension. The intermediatering 49 is screwed on before inserting the respective insertion cap 48in the direction towards the bevel roller bearing 44 and it is securedby means of a safety sheet 51 also set onto the shaft 42 in its screw-onposition.

The attachment of the insertion caps is implemented by respectivescrews, which attach the insertion caps 48 at the respective ends of theshaft 42. The shaft ends 69 are received by conically formed plug-onbores 68 of the insertion caps.

The respective adjusting lever end 48, 49 is arranged between a restflange 50 formed on the ends 53 of the insertion caps 48 pointing awayfrom the shaft 42 and ends of the respective transverse bore 41. Itcomprises, see also FIG. 5, fork ends 65, 66, which are arranged on bothsides of the respective bearing block 32, 39. In order to fix the forkends on the respective insertion cap 48, this cap comprises at least onescrew bore 52, through which a respective screw can be screwed in up tothe fork ends.

The structure of the second bearing block 39 is analogue. Furthermore,it must be noted with respect to the second bearing block, that withthis block the extended end 17 of the spindle 16 is detachably attachedby means of a respective screw, see FIG. 3.

Cooling ribs 70 are arranged on an outer side of the drive housing 28,see the dotted illustration in FIG. 2. The cooling ribs may be attachedboth in the longitudinal direction and in the radial direction. Otherarrangements are also possible.

Furthermore, at least one lubricant supply channel is shown as part of alubricant distribution system 60, through which said channel lubricantcan be supplied from the outside to the screw thread drive with theradial and axial bearing means and to the bearing means formed by thebearing blocks 33.

In FIGS. 4 and 5, which correspond to a top plan view or bottom view ofthe drive device 1 according to FIG. 1 according to the invention, guiderods 55 and 56 can particularly be seen. These rods serve for receivingmoments of tilt and torques transmitted onto the drive device 1 whenoperating the welding tongs. The guide rods extend in parallel to thelongitudinal direction 40 of the spindle 16 within the drive housing 18.In this housing respective longitudinal bores 58, 59 are formed inextension of the adjusting lever ends 8, 9 and fork ends 65, 66,respectively. On ends 57 of the guide rods 55, 56, the rods are attachedat the drive housing 18.

FIG. 6 shows a longitudinal section through a second embodiment of thedrive device according to FIG. 1 according to the invention, withidentical components as in FIG. 2, wherein some details referring to thewelding tongs per se are not shown.

Only the substantial differences between the two embodiments will now bedescribed.

In FIG. 6 the spindle 14 is arranged in a spindle sleeve 54, whichextends between the rotating nut 13 and a rotary cap 84. The rotary capis associated to the position transmitter 31, so that this transmitterdetermines via the rotation of the rotary cap to a respective rotaryposition of the spindle sleeve 54 and the rotating nut 13, respectively,and thus the spindle 14.

The spindle sleeve 54 comprises a stepped section 87 on its end pointingtowards the rotating nut 13, said stepped section projecting radiallytowards the outside. The rotor 26 is arranged on an outer side of thespindle sleeve 54 in the area of the servo motor 21, and this rotor canbe rotated together with the spindle sleeve 54. To attach the rotor 26in the spindle sleeve 54 a ring element 91 is arranged on an outer sideof the spindle sleeve between which and a radially outwardly projectingflange of the rotary cap 84 the rotor 26 is fixed for co-rotation.

An intermediate ring 88 is arranged adjacent to the rotor 26. Betweenthis ring and the radially outwardly projecting stepped section 87 abearing means 85 is arranged for the rotatable support of the spindlesleeve 54 within the drive housing 18.

For further fixing the bearing means 85, an additional attachment ring86 is provided, which is detachably attached for instance by means ofscrews at the drive housing 18 in the area of the stepped section 87.The attachment ring 86 at the same time serves for the radial androtatable support of the stepped section 87.

The rotating nut 13 is attached within the stepped section 87particularly in the area of its front side 29 so that the rotating nut13 rotates together with the spindle sleeve 54 but is undisplaceable inthe axial direction.

FIG. 6 shows the lubricant distribution system 60 through which thelubricant may be supplied from the outside particularly to the screwthread drive 12.

In order to be able to ventilate the bellows 35 as protective means 34during moving the spindle 14 in and out, a ventilation means 89 isprovided which connects an interior of the bellows with the outerenvironment of the drive device 1 via lines 91, one of which beingshown, as well as via air exchange dampers 92.

FIG. 1 further shows a schematic view of welding tongs 1 with two leversor limbs 2, 3.

The embodiment of the welding tongs shown is an example of so-calledX-welding tongs.

A fixing means 72 in the form of an actuator means 74 is associated atleast to one limb 3. This actuator means extends between a fixed point71 and the respective limb 3. A selectable locking position 73 of thelimb 3 can be defined by the locking means 72 and the actuator means 74,respectively. This applies analogously also for other welding tongs, forinstance C-welding tongs.

Of course, it is also possible to analogously arrange a respectivefixing means or actuator means additionally or alternatively on theother limb.

The actuator means (74) (secondary drive) is structured analogously tothe drive device I as a main drive, wherein both may differ in power ormaximal power development.

FIG. 7 shows another embodiment of the drive device 10 and the lockingmeans 72 and actuator means 74, respectively. In this embodiment, thedrive device 10 and the actuator means 74 are integrated in an adjustingmeans 75.

The adjusting means 75 substantially comprises two adjusting elements76, 77, which are movable by respective screw thread drives 78, 79 withthe associated spindles 81 independent of one another in the axialdirection of the respective spindles. The rotation of the respectivespindles 81 can be implemented analogously to FIG. 2, i.e. by using therotating nut 13 and the electric motor-driven drive 21. A respectiverotating nut and a respective electric motor-driven drive is associatedto each screw thread drive 78, 79.

A respective limb 2, 3 is arranged at each adjusting element 76, 77,wherein no joint connection or another movement connection existsbetween the limbs 2, 3 of the welding tongs 3. That means that the limbs2, 3 are movable independent of each other.

The adjusting elements 76, 77 may substantially also be formed as abearing block 32, 39, see FIG. 2, wherein, however, a separate spindleand thus a separate screw thread drive 78, 79 is associated to eachbearing block.

In order to be able to monitor and control the adjustment of each screwthread drive and thus of each limb 2, 3, respective position sensors 83are associated e.g. to the respective adjusting element 76, 77. Theallocation of the position sensor can, however, also be implementedaccording to FIG. 2, see reference numeral 31 for the respectiveposition sensor. The position sensor 31 according to FIG. 2 detects forinstance a respective rotary position of the rotor sleeve 27 andspindle, respectively, wherein each of the position sensors ispreferably formed as an absolute value transmitter.

In the embodiment according to FIG. 7, it is also possible as analternative that only one spindle 82 and accordingly only one screwthread drive 78, 79 is provided. The adjusting elements 76, 77 areassociated to different spindle sections, which are arranged in axialdirection 90 in juxtaposition. The spindle sections may for instancediffer by thread pitch and in any case they comprise a different threadorientation so that when rotating the spindle 81 in a direction ofrotation, the adjusting elements 76, 77 movably connected to the spindleadjust in opposite axial directions 80.

Besides a simple tongs compensation a torque compensation is alsoenabled by the invention particularly by means of the separate lockingmeans 72 or by means of the locking means integrated in the drive device1. The latter for instance leads to the fact that the welding tongs 4,see FIG. 1, are less loaded by respective torques in the area of theirpivot axis.

The drive device 1 according to the invention has an extremely smallconstruction length, see FIG. 2, wherein in the return direction 15 ofthe spindle 16 the screw thread drive 12 as well as the servo motor arearranged substantially fully within the drive housing 18. Furthermore,the drive device I is extremely compact, since the guide rods 55, 56 areintegrated in the drive housing 18. Due to the use of the electric motordriven drive in connection with the screw thread drive 12 a simplepossibility of adjusting the levers of the welding tongs is created,wherein the adjustment is implemented in an accurate manner precisely toreproduce. All intermediate positions between the welding position andthe standby position, see FIG. 1, the levers of the welding tongs 4, canbe adjusted in a controlled manner so that for instance the weldingtongs after terminating a welding process and moving to the next weldingposition must be opened only as far as necessary. Furthermore, besidesthe positions of the levers or welding electrodes, the electrode powerand the respective changes of the electrode power can be measured bymeans of the drive device 1 according to the invention.

1. Drive device (1) for welding tongs (4) comprising particularly a pairof limbs (2, 3), said drive device (1) being arranged substantiallybetween two adjusting ends (8, 9) of the limbs opposing the welding ends(6, 7) provided with the welding electrodes (5) for adjusting at leastone limb (2, 3) between the welding and the standby position (10, 11),characterized in that the drive device (1) comprises a electricmotor-driven screw thread drive (12) with a rotating nut (13) and aspindle axially adjustable between the extended position and the returnposition (14, 15), said spindle with its free extended end (17) beingmovingly connected with an adjusting end (8, 9) of a limb (2, 3). 2.-51.(canceled)